It is possible that the Celtics have found out that the best players are the ones that can deliver results within the team culture - those are the best players.
There are players who buy into the team culture, but can't deliver results - these guys are expendable.
Also, there are players who can deliver results, but not in the team culture - second best but need to leave.
Finally, there are players who cannot deliver results and are not in the team culture-don't even go there.
The question should be, which quadrant would Upshaw fit in?